Rudy Guede, 22, who was sentenced to 30 years in jail, admits being in the house where Kercher was killed but says he had nothing to do with her fatal stabbing and sexual assault, the Italian news agency ANSA reports.
"I want the Kercher family to know that I was not the one who raped and murdered their daughter," Guede said in a prepared statement.
His appeal is being heard during a two-day break in the separate trial of Kercher's U.S. roommate Amanda Knox and Knox's former boyfriend Raffaele Sollecito.
Guede said he was in the bathroom listening to his iPod when he "heard a piercing scream."
He said he saw Knox fleeing the crime scene with a man he could not identify.
The prosecution is scheduled to present final arguments against Knox and Sollecito on Friday.